A Step Farther Out Read Online Free PDF Page B

consist of the West as an island of poverty in the midst of a vast sea of misery. Style, to me, means that everyone on earth has a chance at wealth—at least at a decent life.
    Can we not agree that if everyone on Earth had the per capita metal production of the US, we would probably have achieved world riches? Especially since we export much of ours to begin with; surely it's enough?
    Thus we take our 315 million tons and multiply by the world population, then divide by the US population; assume 3% ore, and we find how much we'll need. The result works out to a sphere less than four miles in diameter—and there are well over 100,000 asteroids larger than that.
    Three percent ore is no bad guess as to what they're made of, either. Actually, given the data from the Moon racks, 3% is an underestimate of the usable metal content of the average asteroid. We've had heavy nickel-iron meteorites fall that were nearly 80% useful metal. Then too, some of the asteroids were once differentiated—that is, they were large enough that metallic cores formed. Then over the last four billion years the planetoids got bashed around until a lot of the useless exterior rock was knocked away, leaving the metal-rich cores exposed where we can get at them.
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Figure 7
CALL SMYTHE, THE SMOOTHER MOVER. . .
    Take one each, FIVE BILLION TON asteroid. Move from the Belt to Earth orbit.

Requires a velocity change of 7 kilometers a second.

KE = V 2 M V 2

or, we need 1.225 x 10 27 ergs.

For reference, the world annual energy use is 10 29 so we're using about 1% of it . . . .

That's also 30,000 megatons.
And 30,000 one megaton bombs might just do it.

For a slightly more efficient system, we can get the energy by converting 2,000 tons of hydrogen to helium . . .
Once we have the rock in Earth orbit, it's simple to get the metal out. We merely boil the entire rock. Of course that takes rather large mirrors, but what the heck. . . .
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    Over 100,000 asteroids, each capable of supplying the world with more metal per person than the US consumes in a year. Surely we won't run out of metals—but can we use them?
    Sure we can. First, for the moment let's forget that the asteroids are way out there in the Belt, and concentrate on how to get the metals out assuming we have the rocks in Earth orbit. That turns out to be easy. We can use sophisticated methods, but there's also brute force: boil the rock
    It takes about 2000 calories per gram to boil iron. That's about the worst case for us, so we'll imagine the entire asteroid is made of iron. It takes, then, about 8.8 x 10 ergs, or twenty thousand megatons, to boil it all away.
    The sun delivers at Earth orbit about 1.37 million ergs a second per square centimeter, and out in space we can catch that with mirrors. To boil our rock we could put up a mirror 80 kilometers in radius. That's too big; but we don't have to boil it all at once. A much smaller mirror to focus the sun onto a small part of the rock would be preferable.
    A space mirror need be nothing more than the thinnest aluminized Mylar, spun up to keep its shape. There's no wind or gravity in space. A mirror one or two kilometers across is a relatively simple structure—and more than adequate for our job. If need be we can actually distill off the metals we want.
    Note, by the way, that there's been absolutely no pollution of Earth so far—even though we've got metals for the entire world. All the waste is out in space where it can't hurt us. But we do have a problem. My metals are not in Earth orbit; they're out there in the asteroid Belt, and they've got to be moved here—and that's going to take energy.
    Let's see just how much it does take. To get from Ceres to Earth you need a velocity change of about 7 kilometers a second. By definition energy is mass given a velocity change, so we can quickly figure out how much; if we move the entire rock it comes to about 1% of the world's energy budget. That's not so much;